Why duplicate copies of some songs on iPad playlists

I have a MacBook Pro (Retina, 15-inch, Late 2013) with BigSur version 11.7.10. 

The MacBook Music version is 1.1.6.37.

I have an iPad (9th gen) with IOS 18.1.1. 

I keep my master music library on this Mac. The songs were virtually all ripped from CDs. 

I also have about 20 Playlists on the Mac.

The iPad has several of these playlists that I sync from the Mac.

On the iPad, some (not all) of the Playlists have some or all of the music doubled up (two copies). 

I assumed that because my Mac OS and iPad OS were a bit outdated that if I updated the OS’s and re-synched the iPad that the Playlists would clean up.

Today I updated my Mac OS and the iPad iOS.

Then I synched the iPad with the Mac and removed the offending Playlists from the iPad.

I then re-synched and re-added the playlists to the iPad. The doubled up lists still were incorrect.

The original playlists on the Mac do not have this doubling. 

Any suggestions why this happening and how to correct it?